In particular with regard to mobile communication systems and/or networks, such as based on a GSM (Global System for Mobile communications), UMTS (Universal Mobile Telecommunication Systems), WCDMA (Wideband Code Division Multiple Access) and/or CDMA 2000 standard there is the tendency, that more and more frequency bands are opened up and/or being licensed resulting in a permanently increasing need to design corresponding radios.
However, classically, for every new frequency band an individual radio has to be designed that forces a complex infrastructure and terminal vendors have to develop a great variety of products, in particular in terms of base stations and/or user terminals, such as handsets adapted to be used within those communication systems.
Thus, especially regarding radio platforms of the 3G+ generation (3G+) of mobile communication systems, there is an objective to design radios, which work in several communication bands and hence, to establish for instance, multiband and/or multistandard mobile communication systems.
As a consequence, there is a significant need for oscillators, which can be tuned across a wide frequency range, wherein the requirement for a wide frequency range directly maps into a wide range for the tuning capacity in the oscillator.
Until today, so-called “varicap diodes” commonly are used for covering a certain tuning range. However, such varicap diodes are limited in terms of their variable capacity, which is rationed from the lowest to the highest value. Based on the drawback of the limited tuning range for the capacity, typically, several individual oscillators are implemented to respectively cover one sub-band by one oscillator, as indicated by the appended FIG. 3. However, an implementation of several oscillators is very cost consuming and additionally results in unwanted complexity and board space to a radio design.
Moreover such varicap diodes do not offer isolation between the signal path and the control path causing additional unwanted noise. Consequently, since the varicap diode merely has two connectors, typically a Bias-T is needed to isolate the control voltage from the oscillator signal. However, one of the most shortcomings based on such a Bias-T is, that the Q-factor of the resonator is degraded, since additional parasitic effects are introduced, in particular due to the additional Bias-T incorporated thereby raising noise of the oscillator.
Furthermore, the Bias-T adds some unwanted parasitics to the resonance circuitry and changes the frequency versus tuning-voltage slope of the oscillator.
Moreover, the capacitance of a varicap diode is determined by the width of the depletion area. Below the reverse breakdown voltage, this depletion area is not completely free of charges and charge fluctuations. This causes additional noise and limits the Q-factor.
An object of the invention is therefore to provide, in particular with regard to the above discussed state of the art, a new and improved approach for enabling an increased high-frequency and/or radio-frequency tuning range by a reduced complexity and board space even with regard to multiband and/or multistandard purposes, in particular suitable within the radio design for mobile communication systems and/or networks, advantageously by simultaneously reducing the undesirable parasitic influences.
Advantageous embodiments or refinements are the subject matter of the respective dependent claims.
Accordingly, the invention proposes a device for high-frequency and/or radio-frequency tuning comprising within one IC-package a first variable capacitor and at least one second capacitor, at least one signal path connected to the first variable capacitor and providing at least one input and one output port and at least one controllable switching means for individually connecting and disconnecting at least one of the at least one second capacitor into the signal path or from the signal path.
Each of the at least one second capacitors may be designed as being a fixed or a variable capacitor, respectively, based on respective specific intended applications.
One of the main advantages achieved thereby is, that due to the splitting of an intended variable capacitance which usually has to cover a wide tuning range into a first variable capacitor or varactor, which may have a small tuning range, and at least one second capacitor, which can be individually connected and disconnected into the signal path or from the signal path by switching means, advantageously in parallel to the first variable capacitor, the provided inventive device enables a significantly enhanced tuning range for the entire capacity and hence, an increased ratio between the lowest and the highest capacity value can be achieved.
In addition, due to the integration of all these components into one IC-package the dimensions are extremely small with regard to the high frequencies to be tuned and/or matched and hence high frequency signal based parasitic effects caused by large transmission lines going on- and off-chip with individual components are significantly reduced.
Furthermore, due to the integration of the realized inventive varactor with extended tuning range into one IC-package, there is only a very low amount of board space necessary to cover a variety of tuning and matching tasks.
Moreover, even with regard to multiband and/or multistandard purposes the invention provides a cost saving and board space saving solution, since the implementation of several individual tuning devices which would have to be switched at their respective output for respectively covering one sub-band is avoided.
Additionally, by the incorporation of the inventive tuning device into an rf-system, sensitive rf-parameters may easily be tuned for optimization purposes, instead of individually designing and optimizing a plurality of matching circuits. This enables, in particular with regard to the manufacture, a significant reduction of development costs and the possibility of compensating tolerances. Moreover, the redesign of critical circuits, for example due to a replacement of certain components usually resulting in time and cost consuming modifications of the circuitry layout, can often be avoided.
By using controllable switching means with an actuator and a contact element to close or open the switching means for the individually connecting and disconnecting and advantageously by using for a variable capacitor an actuator for driving a movable element of the variable capacitor to vary the effective area thereof, in particular by changing the distance between at least two plates or the degree of engagement of fingers of a comblike structure, it can be easily ensured, that the at least one control signal path for controlling the switching means and/or for tuning the variable capacitor can be isolated from the high frequency signal path.
According to advantageous embodiments, the at least one control path comprises means for digitally controlling a plurality of switching means individually and/or the at least one control path, in particular for controlling the switching means is connectable to an EPROM or EEPROM, to a FPGA (Field Programmable Gate Array) and/or to an ASIC (Application Specific Integrated Circuit), so that application specific and/or desired operating conditions of the inventive device can be set and/or retrievable stored.
Furthermore, the tuning or control path for controlling a tunable capacitor is practically adapted to be controllable via an analogue voltage or via a digital to analogue converter.
For the praxis, it is suggested, to provide a separate control path for a tunable device and/or at least one control bus for controlling a plurality of fixed capacitors by means of the respective associated switches.
To further increase the overall capacity tuning range, it is proposed to arrange at least two second capacitors, such as fixed capacitors for example, in logarithmic scale, wherein the variable first capacitor at least is adapted to match the lowest range of the logarithmic scale, thereby simultaneously providing the possibility to reduce the individual scale spacing steps there between.
According to an advantageous refinement, in particular for simplifying the integration within one IC-package it is proposed to fabricate the inventive device by using a so-called Micro-Electro-Mechanical-Systems (MEMS) technology.
By using such MEMS technology all internal parasitics are well defined and in comparison with the state of the art a production spread usually is avoided. The invention proposes further to produce the tunable components and/or the switches as three-dimensional mechanical structures, in particular by employing a bulk micro machining and/or a surface micro machining technology.
Based thereon, a controllable switching means is advantageously realized by using a MEMS switch. Correspondingly, the at least one tunable or variable capacitor incorporated within the inventive device is based on a MEMS-Varactor.
However even the incorporation of a switching means and a respectively associated second variable capacitor into one common MEMS-component is proposed, such as for example by designing a rocker means having a linear rock range for providing the variability and a non-linear rock range for providing a switch-off function. Based thereon, the resistance of a separate switch means is additionally avoided.
According to advantageous embodiments the actuating mechanisms means respectively comprises a mechanism based on electrostatic, piezoelectric, thermal, magnetic or bimetallic actuator functionality.
A further advantage of providing the inventive device, as a MEMS-based device is, that the technology for the varactor and the switching means is of the same type. Moreover, even such a MEMS-based device provides the possibility for an easy combination with further circuits, especially application specific circuits, based on Silicon, CMOS and/or BICMOS (Bipolar-CMOS) technology for example, especially allowing the integration of some control logic for a digital port or an active rf-signal circuit.
As a consequence, by advantageously using the technique of Micro-Electro-Mechanical-Systems (MEMS) for the integration of capacitors, varactors and high frequency-switches into one IC-package, a versatile electrical device for tuning a wide high-frequency range and even for matching purposes is provided, with the advantages of a low noise of the tunable capacitor of a very high isolation between the controlling paths and high-frequency paths. Hence, low tolerance components with well defined internal parasitics are achieved, wherein the complete inventive configuration can be utilized for covering reconfiguration, optimization or tuning purposes within a wide capacity and/or frequency range and hence can be used in several application areas. Such an advantageous application areas are especially the use within a communication system and/or network, in particular a mobile communication system and/or network based on a GSM, UMTS, WCDMA and/or CDMA 2000 standard, within an oscillator, in particular adapted for use within a receive and/or transmit radio unit of a mobile communication system, within a base station or within a user terminal in particular adapted for use within a mobile communication system.
It should be emphasized that the drawings of the instant application are not to scale but are merely schematic representations, and thus are not intended to portray the specific dimensions of the invention, which may be determined by skilled artisans through examination of the disclosure herein.